The WCDMA, as a trend of mobile communication development, is one of three major 3rd generation (3G) mobile communication systems in the world at present. In view of long-term co-existence between a GSM system and a WCDMA system, it is necessary to realize radio transmission mode compatibility between the WCDMA system and the GSM system.
Along with development of 3G mobile communication technology, standardized baseband-radiofrequency interface turns out to be an increasing attention of manufacturers, and interface standards, such as Common Public Radio Interface (CPRI), Open Base Station Architecture Initiative (OBSAI) and the like, successively appear in recent years. Jointly developed by Ericsson, Huawei, NEC, NORTEL and Siemens, the CPRI protocol formulated for baseband-radiofrequency in radio communication base station are supported by most of manufacturers due to its economical efficiency and ease of use. CPRI protocol is developed mostly according to the standard of the WCDMA system, thus frame data of WCDMA system can be organized completely according to CPRI structure.
As shown in FIG. 1, when a CPRI rate is 1.2288 Gbps, first 16 bit in each CPRI Base Frame (BF) is used for transmitting signaling data and the latter 15*16 bit is used for transmitting In-phase/Quadrature (IQ) data. As shown in FIG. 2, when the CPRI rate is 2.4576 Gbps, first 32 bit in each CPRI BF is used for transmitting signaling data, the latter 15*32 bit is used for transmitting IQ data. At different CPRI rates, the durations of BFs are the same, and 256 BFs form 1 Hyper Frame (HF) of CPRI, 150 HFs aforementioned form a 10 ms CPRI radio frame, thus the duration of the CPRI BF is 25/96 μs.
As shown in FIG. 3, when the CPRI rate is 1.2288 Gbps, IQ data area of each 240 bit of CPRI BF is divided as 8 Antenna-Carrier (A×C) subchannels; each A×C subchannel is 30 bit. As shown in FIG. 4, when CPRI rate is 2.4576 Gbps, IQ data area of each 480 bit of CPRI BF is divided as 16 A×C subchannels; each A×C subchannel is also 30 bit
The CPRI rate is defined as high rate, such as 1.2288 Gbps, 2.4576 Gbps and the like, according to CPRI protocol, while the character rate of burst pulse for transmitting data is defined as only 270.833 kbps by the regulation of GSM system. Therefore, it is a crucial concern that how to make different data rate modes between two different standards into a general system for designing dual-mode base stations comprising of the WCDMA system and the GSM system. Existing methods for realizing compatibility between the WCDMA system and the GSM system are realized by switching between two codes without unification in the bottom layer, which are not called as a genuine compatibility between the WCDMA system and the GSM system.